Molten steel frequently contains alumina and other material as an impurity. Unless the alumina is removed it becomes an undesirable inclusion in the poured steel, hence diminishing its value. A particularly troublesome problem with alumina inclusions in steel contained in tundishes is that over a period of time the alumina inclusions tend to plate out in the area around and within the pouring nozzles located at the bottom of the tundishes. These deposits build up and cause a blockage or a restriction in the flow of molten steel being poured from the tundish. The alumina selectively plates out on and in the nozzles since they are usually constructed of alumina and do not have smooth surfaces such as are often found in the side walls of the tundish. It is the chemical compatibility of the nozzle that promotes the adhesion of Al.sub.2 O.sub.3 inclusions to the nozzle.
Tundishes can arbitrarily be divided into three classes. The first are of large dimension and are used to pour slabs. These tundishes usually have one nozzle. Medium and small tundishes are used to cast blooms and billets respectively. These smaller tundishes may contain from two to eight pouring nozzles.
Until the present invention, the removal of alumina has been accomplished by allowing the alumina along with the other impurities in the molten steel impurities to float to the surface of the steel as slag. This method is not entirely satisfactory since if within the tundish there is poor circulation of the molten steel, the impurities do not float to the surface and become slag.
In order to improve the circulation of liquid metal into "dead spaces," and thereby increase the residence time of the liquid metal, tundishes have been developed in which the metal flow is diverted using barriers. These barriers are usually, but not necessarily, substantially rectangular in cross-section and extend between the tundish walls in a direction which is transverse to the prevailing flow of metal, between the metal entry and exit points. One type of barrier, which is commonly called a weir, is located at the upper part of the tundish walls and prevents liquid metal from flowing continuously across the surface of the metal bath while permitting the liquid metal to flow underneath the weir. Another type of barrier, which is commonly called a dam, is located between the tundish walls at the lower part thereof and protrudes from the tundish floor. The flow of liquid metal in a tundish which is equipped with a dam is directed to move over the surface of the dam. Dams and weirs may be used together to improve circulation. The third and most effective devices for improving circulation in tundishes are baffles which are barriers which contain openings below the normal surface level of the molten steel in the tundish.
When the alumina restricts the nozzles of the tundishes another method used to alleviate this problem is to manually rod out the alumina build-up. This procedure is labor intensive and often tends to cause a breakage or chipping of the ceramic pouring nozzles located at the bottom of the tundishes. Also portions of the Al.sub.2 O.sub.3 will end up in the mold and consequently in the final product as the result of rodding.
If it were possible to provide an improved method for removing alumina from molten steel in tundishes, which method was simple and efficient and which thereby prevented the plugging of tundish nozzles, a valuable contribution to the art would be afforded.